Gas turbine engines operate to produce mechanical work or thrust. Land-based gas turbine engines typically have a generator coupled thereto for the purposes of generating electricity. There are a number of issues that affect the overall performance and durability of the engine components, especially the combustion section. The combustion process creates varying pressure oscillations and dynamics in the combustion hardware that can result in significant wear. Specifically, the pressure oscillations can cause mating hardware to vibrate and move relative to one another. Excessive combustion dynamics can cause premature wear of mating hardware such that the hardware must be repaired or replaced.
Typically, gas turbine engines comprise multiple fuel circuits, depending on the quantity and location of the fuel nozzles as well as the combustor operating conditions. For example, a General Electric Frame 7FA gas turbine engine that utilizes a dry-low NOx (DLN) 2.6 combustor, has six main fuel nozzles per combustor and additional fuel injectors located radially about the combustor case, known as quaternary nozzles. A different quantity of these fuel nozzles operate together as the engine increases and decreases in power in an effort to minimize oxides of nitrogen (NOx) emissions and combustion dynamics in the combustor. For this engine design, there are four different fuel circuits associated with the different nozzles, PM1, PM2, PM3, and quaternary, with each circuit requiring a specific fuel flow rate depending on the operating conditions. This division of the fuel within the fuel circuits to a comply with a particular required fuel flow rate is referred to herein as a “fuel-flow split.”
As such, employing a method to adjust, or bias, fuel-flow splits based upon changes in the density of the air entering the combustor, where unchecked air-humidity fluctuations typically adversely affect combustion dynamics, would improve the reliability and emissions performance of the gas turbine engine.